Multidirectional retroreflectors and methods of reflecting light beams from multiple directions are provided. The multidirectional retroreflectors utilize a four-mirror retroreflector with a common virtual reflection point.
|
7. A multi-directional retroreflector comprising:
a mirror;
a retroreflector, wherein the mirror is positioned to reflect a light beam onto the retroreflector and wherein the optical path length to the retroreflector from the mirror is equal to the optical path length from the retroreflector mirror to a virtual position; and
a cubic, spherical or cylindrical manifold, wherein the mirror and the retroreflector are adjustably mounted to the manifold by an adjustable mount.
14. A method of reflecting one or more light beams from multiple directions comprising:
reflecting a light beam off of a mirror and onto a retroreflector mounted on a manifold at a first position; and
moving the retroreflector to a second position on the manifold and reflecting a light beam off of beam off of the mirror and the retroreflector mounted at the second position by an adjustable mount, wherein the retroreflector in the first position and the retroreflector in the second position have the same virtual point.
1. A multi-directional retroreflector comprising:
a first mirror;
a first retroreflector, wherein the first mirror is positioned to reflect a light beam onto the first retroreflector and wherein the optical path length to the first retroreflector from the first mirror is equal to the optical path length from the first retroreflector mirror to a virtual position point; and
a second retroreflector, wherein the second retroreflector is positioned at one of the virtual position or is positioned point and a position away from the virtual position at a position that has the same optical path length as the optical path length to a second mirror point, wherein, in the position away from the virtual point, the optical path length to the second retroreflector from a second mirror is equal to the optical path length from the second mirror to the virtual point.
19. A method of reflecting one or more light beams from multiple directions comprising:
reflecting a light beam off of a first mirror and onto a first retroreflector, wherein the optical path length to the first retroreflector from the first mirror is equal to the optical path length from the first retroreflector mirror to a virtual position point; and
reflecting a light beam off of a second retroreflector, wherein the second retroreflector is positioned at one of the virtual position or is positioned point and a position away from the virtual position at a position that has the same optical path length as the optical path length to a second mirror. point, wherein, in the position away from the virtual point, the optical path length to the second retroreflector from a second mirror is equal to the optical path length from the second mirror to the virtual point.
0. 25. A distance measuring device comprising:
a first reflective surface;
a first reflector, wherein the first reflective surface is positioned to reflect electromagnetic waves onto the first reflector and wherein the path length to the first reflector from the first reflective surface is equal to the path length from the first reflective surface to a virtual point; and
a second reflector, wherein the second reflector is positioned at one of the virtual point and a position away from the virtual point, wherein, in the position away from the virtual point, a second reflective surface is positioned to reflect electromagnetic waves onto the second reflector and the path length to the second reflector from the second reflective surface is equal to the path length from the second reflective surface to the virtual point.
0. 37. A method of reflecting at least two electromagnetic waves from multiple directions comprising:
reflecting a first electromagnetic wave off of a first reflective surface and onto a first reflector, wherein the path length to the first reflector from the first reflective surface is equal to the path length from the first reflective surface to a virtual point; and
reflecting a second electromagnetic wave off of a second reflector, wherein the second reflector is positioned at one of the virtual point and a position away from the virtual point, wherein, in the position away from the virtual point, a second reflective surface is positioned to reflect electromagnetic waves onto the second reflector and the path length to the second reflector from the second reflective surface is equal to the path length from the second reflective surface to the virtual point.
0. 50. A method of reflecting at least two electromagnetic waves in multiple directions virtually originating from a common point comprising:
reflecting a first electromagnetic wave from a first reflector off of a first reflective surface in a first direction beam, wherein the optical path length from the first reflector to the first reflective surface is equal to the optical path length from the first reflective surface to a virtual point; and
reflecting a second electromagnetic wave from a second reflector in a second direction beam, wherein the second reflector is positioned at one of the virtual point and a position away from the virtual point, wherein, in the position away from the virtual point, a second reflective surface is positioned to reflect the second electromagnetic wave onto the second reflector and the optical path length from the second reflector to the second reflective surface is equal to the optical path length from the second reflective surface to the virtual point;
wherein the first direction beam and the second direction beam intersect at the virtual point.
2. The multi-directional retroreflector of
3. The multi-directional retroreflector of
4. The multi-directional retroreflector of
6. The multi-directional retroreflector of
9. The multi-directional retroreflector of
10. The multi-directional retroreflector of
11. The multi-directional retroreflector of
22. The method of
23. The method of
24. The method of
0. 26. The distance measuring device of
0. 27. The distance measuring device of
0. 28. The distance measuring device of
0. 29. The distance measuring device of
0. 30. The distance measuring device of
0. 31. The distance measuring device of
0. 32. The distance measuring device of
0. 33. The distance measuring device of
0. 34. The distance measuring device of
0. 35. The distance measuring device of
0. 36. The distance measuring device of
a probe located at the virtual point; and
a mount for mounting the first reflector, the first reflective surface, and the probe together.
0. 38. The method of
0. 39. The method of
0. 40. The method of
0. 41. The method of
0. 42. The method of
0. 43. The method of
0. 44. The method of
0. 45. The method of
0. 46. The method of
0. 47. The method of
0. 48. The method of
0. 49. The method of
0. 51. The method of
0. 52. The method of
0. 53. The method of
0. 54. The method of
0. 55. The method of
0. 56. The method of
0. 57. The method of
0. 58. The method of
0. 59. The method of
0. 60. The method of
0. 61. The method of
0. 62. The method of
0. 63. The method of
|
|||||||||||||||||||||||||||
This application claims priority to U.S. Provisional Application No. 60/536,520 entitled “Attenuated Retroreflector” filed Jan. 15, 2004, the entirety of which is specifically incorporated by reference.
This invention was made, in part, with funding from the United States Government under Award No. AST-0223851 and, accordingly, the United States Government may have certain rights in this invention.
This invention relates to multidirectional retroreflectors. More specifically, this invention relates to multidirectional retroreflectors which use a four-mirror retroreflector with a common virtual reflection point.
Large-scale metrology includes the measurement of coordinates over large distances, for example greater than the volume of a conventional coordinate measurement machine (CMM), which is typically limited to a cube of a few meters. There are many instances, for example in the aircraft industry, radio telescope and linear accelerator applications where measuring such distances is preferably accomplished with a high degree of accuracy. There are also field measurements of smaller scale which do not lend themselves to placement in a CMM, such as in situ measurements of machinery, outdoor measurements, shop floor measurements, etc.
The measurement of coordinates is typically accomplished by measuring a distance and two angles, as with a conventional surveying total station or laser tracking interferometer; the measurement of three orthogonal distances, as with a CMM; the measurement of angles from two locations on a known baseline, such as with theodolites; the measurement of spacing on a two-dimensional image projection from multiple locations, as with photogrammetry; the measurement of distance from three, or more, known locations on a baseline, as with multilateration; and various other manners.
One way to measure distances accurately is by using laser interferometry. In laser interferometry a coherent, monochromatic light beam from a laser is split into two beams using a beamsplitter. One beam, the reference beam, is focused onto a photosensitive detector. The second or measurement beam, is allowed to travel through space and strike a reflector positioned in space at the first of two measurement points. The reflector is adjusted to return the reference beam to the surface of the photosensitive detector. Here the reference and reflected measurement beams interfere. The target reflector can then be moved to the second point to be measured. As the target moves, the reflected measurement light beam is continuously focused onto the photosensitive detector, interfering with the reference beam. By electrically measuring the periodic variation of the detector output, one can measure differential lengths from the initial target position as multiples and fractions of the wavelength of the illuminating source.
In all of these laser interferometry devices, the reflective target is preferably oriented to return the reflected measurement beam to the photosensitive target of the detector from a wide range of beam angles. Typically, a retroreflector, such as a hollow three-mirror reflector, comprised of three carefully aligned orthogonal mirrors (typically on the order of one arc second), is used to return the beam. The retroreflector may have slightly less accuracy than a single flat mirror but only requires that the operator align the device so as to point towards the detector within a cone of perhaps 30-40 degrees in width. The reflected beam from the retroreflector undergoes reflections from all three orthogonal mirrors and has the interesting property that the return beam will emerge traveling parallel to the incoming beam, in the opposite direction, and displaced from the incoming beam by a distance of twice the distance from the incoming beam to the retroreflector apex, i.e., symmetrically about a parallel beam through the apex. The optical path length, and thus the time of flight, is virtually the same as the distance to the retroreflector apex. Therefore, the measurement is physically associated with the physical location of the retroreflector apex.
Electronic distance measurement (EDM) is commonly achieved by measuring the time of flight of an electromagnetic wave, such as a laser beam or microwave radar, to a target retroreflector or the scattered reflection from a passive target. Most conventional surveying instruments employ a retroreflector target in order to clearly define the measurement point, improve the signal-to-noise ratio of the return signal, and thus operate at reduced power. While typically not as accurate as the laser interferometer, EDM offers a major advantage over the interferometer for many applications. Unlike the interferometer, which inherently measures a differential distance—and thus must be used in a fringe counting integration mode to measure between two points without a break in the signal, EDM measures the absolute distance between the instrument and target. Thus, there is no requirement to integrate over a path while physically moving the target retroreflector through the measurement volume. This allows EDM to be used to measure multiple targets by switching between targets at will. The operating range of conventional EDMs are kilometers, while the operating range of typical laser interferometers are less than 100 meters.
A number of laser interferometer and electronic distance measurement applications desire an even wider angle of acceptance or multiple retroreflectors. A problem with using multiple retroreflectors is that not all of the retroreflectors can be located at a common measurement point. When the measurement axis does not pass through the measurement point, the resulting measurements are sensitive to rotations of the object and/or angle between the instrument and object, i.e., the Abbe error (See Ted Busch, Fundamentals of Dimensional Metrology (Delmar, 1988)).
Surveying equipment manufacturers have assembled solid glass retroreflectors, such as the Leica™ GRZ4 360 degree prism. However, as described in L. A. Kivioja, The EDM Corner Reflector Constant is Not Constant, Surveying and Mapping 143-55 (June 1978) and D. C. Hogg, Optical Center of a Glass Three-mirror: Its Measurement, Applied Optics, 15(2):304-305 (February 1976), the glass offset, or extra delay due to the reduced speed of light in glass, is a function of the incident angle, and the coverage overlaps between adjacent retroreflectors, so there is a significant Abbe error for the GRZ4.
Laser interferometers are typically calibrated in a back-to-back retroreflector configuration, where the rotation of the retroreflectors is constrained. For example, the National Institute of Standards and Technology (NIST) has built a Laser Rail Calibration System (Larcs) for calibrating laser trackers against an interferometer on a linear rail. Tracking laser interferometers are discussed in U.S. Pat. Nos. 4,714,339 to Lau et al.; and 4,790,651 to Brown et. al. Larcs uses two spherically mounted retroreflectors (SMRs) (described in more detail below), in a back-to-back configuration on a carriage, to build a bidirectional retroreflector assembly, i.e., one direction fixed for the reference interferometer parallel to the rail, and the other free to rotate in a nest to accommodate the laser tracker under test.
The Abbe error is minimized by mounting the two retroreflectors as close as practical and constraining the carriage to a rail system to minimize rotations of the assembly. However, for portable rails, the uncertainty due to the Abbe error is estimated to be a significant part of the total error budget.
NASA has built custom hollow retroreflector assemblies with a common physical reflection point, and thus eliminated the Abbe error. See Schmidtlin et. al., Novel Wide Field-of-View Laser Retroreflector for the Space Interferometry Mission, Conference on Astronomical Interferometry, Vol. 3350, 81-88, SPIE, 1998 and NASA Jet Propulsion Lab, Wide-Angle, Open-Faced Retroreflectors for Optical Metrology, Photonics Tech Briefs, 15a-16a, (March 1999).
These solve the Abbe error problem for some classes of measurements. However, since these retroreflectors share a common physical point, they sacrifice part of the center aperture, are difficult to build, are difficult to reference to an outside mechanical point, are expensive for routine applications, and the directions are not adjustable.
Gelbart et. al. in U.S. Pat. Nos. 5,305,091 and 5,920,394 describe an “omnidirectional retroreflector” pair combined with a fixed probe. By multilaterating on the pair of retroreflectors, the probe coordinate is calculated. The omnidirectional retroreflectors, described in the '091 patent, “consist of two concentric spheres made of transparent material and having the refractive index of the inner sphere higher than the refractive index of the outer sphere, the outside sphere coated with a partially reflective coating.”
As described by Takatsuji et. al., Whole-Viewing-Angle Cat's-Eye Retroreflector as a Target of Laser Trackers, Measurement Science Technology, 1O:N87-N90 (1999), ideal omnidirectional spherical retroreflectors have recently been built from high index of refraction materials. Unfortunately, the glass is difficult to work, expensive, and the return power is low due to the spherical aberration and small working aperture, as well as the low reflection coefficient of the glass/air interface on the back side of the sphere, i.e., most of the power is transmitted through the sphere.
Laser trackers incorporate a laser interferometer with an automated mirror system to track a retroreflector. The interferometer measures differential range very accurately, with the fundamental limitation being the uncertainty of the index of refraction—which is typically in the 1 ppm range.
The angle measurements are somewhat less accurate. The fundamental limitation is atmospheric turbulence and temperature gradients bending the beam. There are also practical limitations with the encoders, mechanical system, beam quality, gravitational vector reference frame, etc.
Nakamura et al., A Laser Tracking Robot Performance Calibration System Using Ball-Seated Bearing Mechanisms and a Spherically Shaped Cat's-Eye Retroreflector, Review of Scientific Instruments, 65(4):1006-1011, (April 1994), points out that for a distance measurement uncertainty of δr, in an ideal orthogonal trilateration measurement, the uncertainty volume is (δr)3. For two angles and a distance measurement, the uncertainty volume is (rδθ)2δr. For example, for a typical distance measurement uncertainty of 1 ppm (δr/r=10−6) and an angle uncertainty of one arc second (˜5×10−6 radians), the trilateration uncertainty, for three equal distances r, the uncertainty volume would be
δν=r310−18
whereas the uncertainty volume for two angles and a distance would be
δν=25r310−18,
or 25 times greater than the trilateration uncertainty volume—hence the inherent potential improvement in accuracy by using multiple distance measurements. In practice, there are two primary obstacles to achieving this huge improvement. Conventional retroreflectors do not support simultaneous measurements in the three orthogonal directions, and in actual field conditions it can be hard to mount an instrument on a stable tower or structure.
U.S. Pat. Nos. 5,530,549 and 5,861,956 to Brown et al., describe a probing retroreflector in which the distance to a probe tip can be determined. In Brown et al. a line between a retroreflector and a probe tip is bisected by a single mirror. The length of the optical path between the mirror and the probe tip is the same as the length of the optical path between the mirror and the apex of the retroflector. The system has allowed the use of retroreflectors in spaces that can not normally be reached by a typical retroreflector. This system, however, does not allow measurements to be simultaneously taken from different directions.
Laser trackers typically use spherically mounted retroreflector (SMR) targets. These are typically hollow or cat's-eye type retroreflectors, with the optical centers carefully located in the center of the spherical mounting—thus allowing the optical measurements to be related to the physical center of the sphere. Hollow SMRs, such as those built by PLX Inc.® are more economical than cat's-eye SMRs, but have a reduced angle of acceptance and thus are more susceptible to dropping the laser interferometer beam while tracking.
An improvement in the accuracy of the laser tracker (or EDM) is to use multiple instruments and/or augment with additional information, e.g., known artifacts, stable bench marks, hydrostatic leveling, or other constraints. For three or more instruments, oriented in the proper baselines, the less accurate angle measurements can be neglected or weighted less in a least squares, or more sophisticated, reduction.
While crosstalk between instruments is not a problem using multiple laser trackers on a common SMR, the relatively small angle limitation of even the cat's-eyes makes the instrument baselines unfavorable for high accuracy multilateration measurements, and of course the Abbe error is the limitation for conventional assemblies of SMRs.
As described by Parker et. al., Metrology System for the Green Bank Telescope, in Proceedings ASPE 1999 Annual Meeting, pages 21-24 (American Society for Precision Engineering, 1999). The Robert C. Byrd Green Bank Telescope large-scale metrology system was designed to operate as a multilateration system employing 18 laser ranging instruments measuring ranges to cardinal points on the moving telescope. While some paths are physically blocked by the structure, it behooves the designers to use multidirectional retroreflectors in order to maximize the number of independent measurements, and thus strengthen the calculation of cardinal point coordinates.
The increasing interest in multilateration, using laser trackers or other EDMs, has created a need for less expensive and more practical multidirectional retroreflectors with zero Abbe error.
In addition, in some retroreflector applications it may be desirable to attenuate the return beam from the retroreflectors. For example, in some electronic distance measurement applications, the dynamic range may be such that the signal is preferably attenuated for close-range measurements in order to avoid non-linearities in the detector electronics.
To account for time of flight or, alternatively, phase shift through the attenuator, any attenuating filter may need correction for the group index of refraction of the attenuating medium. Also, the cosine theta error for the thickness of the filter is preferably avoided. Finally, additional surfaces can introduce additional reflections which can introduce phase errors and make the retroreflector sensitive to orientation.
Broadly described herein are multidirectional retroreflectors and methods and systems for utilizing retroreflectors. The retroreflectors use a common virtual reflection point that is shared by multiple retroreflectors. The same concept can be extended to optical targets by replacing the retroreflector with an optical target.
One embodiment of the invention is directed to a multi-directional retroreflector that includes a retroreflector
from the apex.
The Abbe error, due to the distance between the center of the sphere and the apex can be a problem. The orientation of the three-mirror retroreflector can be established by auto-collimating on each of the retroreflector mirrors, or by building a fixture to fix the orientation. A solid glass retroreflector mounted in a fixture can be used to orient a hollow three-mirror retroreflector. The hollow retroreflector is gently dropped over the inverted glass retroreflector of known geometry and orientation, and thus transferring the known geometry and orientation to the hollow retroreflector, which can then be fixtured.
While the multidirectional retroreflectors can be constructed in a fixed manner, the four-mirror retroreflector assemblies could also be built separately and then the assemblies can be configured individually as needed. For example, by building four-mirror retroreflectors, with a uniform offset and footing, any number of configurations can be configured. The foot could be a fixed attachment or magnetic base to facilitate rapid reconfiguration and adjustment.
For example, an orthogonal coordinate system can be constructed by placing one or more four-mirror reflectors with a flat, three ball or Kelvin mount around a cubic manifold as shown in
A four-mirror retroreflector with a “V” foot could be used to mount an array of retroreflectors on a cylindrical manifold as shown in FIG. 4. In
Finally, three-dimensional coverage can be obtained by a three-mirror retroreflector with a three-point, or conical, nest foot that attaches to a spherical manifold, as shown in FIG. 5. In
Due to the fact that the Abbe error is eliminated, any of the suggested examples could be articulated. For example, an assembly could be mounted on a coordinate measurement machine, rotated about an axis by a motor; or maintained in a fixed orientation, with respect to gravity, by a pendulum counterweight, e.g., to compensate for the rotation in elevation of a radio telescope.
In some application it may be desirable to attenuate the return beam from the retroreflectors. This can be accomplished by modifying a standard three-mirror retroreflector. In the modified design, one of the surface mirrors is replaced with a flat, OD 3 (transmission=10−3), neutral density filter, i.e., instead of reflecting off an aluminized mirror, about 1% of the power is reflected off the front surface of the glass and the remaining power is absorbed by the filter. By using an absorbing type neutral density filter material, the additional reflections off the rear surface are virtually eliminated (the OD 3 filter is effectively an OD 6 for the double pass).
Since all retroreflector beams undergo a reflection at all three mirrors of a three-mirror retroreflector, additional surfaces could also be substituted for compounded attenuations. Alternatively, the first surface mirror in a four-mirror retroreflector can be substituted. Calibration of the retroreflector mechanical apex remains the same, as with the standard three and four-mirror retroreflectors.
Reflections from the front surface of the glass filter, unlike the metal mirrors, introduce polarization rotations which can introduce further attenuation if the detector input is polarization sensitive, e.g., if an isolator is used on the detector. Moreover, the reflection coefficient is angle of incidence dependent. By rotating the retroreflector about the optical axis, the polarization and angle of incidence (and thus reflection coefficient) are modulated, which can be used to adjust the attenuation.
To introduce a transient attenuation, such as when conducting a test of the sensitivity of the distance measurement to signal amplitude, a simple test can be conducted by misting a light fog onto the retroreflector under test. For example; by exhaling on the retroreflector (with proper eye protection), or placing a cup of hot water next to the retroreflector, a light mist will condense on the cool reflecting surfaces which will effectively kill the reflected power. This will rapidly evaporate away. By recording the distance measurement and power levels as the mist evaporates, a plot of distance vs. power level can be constructed.
While the description and examples relate to four-mirror retroreflectors for optical path length measurement, an extension of the concepts would be to replace any or all of the three-mirror retroreflector with an optical target for angle-only measurements, such as with theodolites.
While the examples refer to laser beams, the same concepts and configurations can be adapted for other radiation sources, e.g., microwaves and acoustics.
The above description is presented to enable a person skilled in the art to make and use the invention, and is provided in the context of a particular application and its requirements. Various modifications to the preferred embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the invention. Thus, this invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.
This application discloses numerical range limitations. Persons skilled in the art will recognize that the numerical ranges disclosed inherently support any range within the disclosed numerical ranges even though a precise range limitation is not stated verbatim in the specification because this invention can be practiced throughout the disclosed numerical ranges and at other numerical ranges which persons skilled in the art will find this invention operable.
Other embodiments and uses of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. All references cited herein, including all U.S. and foreign patents, patent applications, all publications and other documentary materials, are specifically and entirely hereby incorporated by reference.
| Patent | Priority | Assignee | Title |
| 10203268, | May 26 2016 | Laura P., Solliday; Sophie, Lin | Methods for measuring and modeling the process of prestressing concrete during tensioning/detensioning based on electronic distance measurements |
| 8209134, | Dec 04 2008 | SOLLIDAY, LAURA P ; Sophie Lin, Trustee of the John Michael Payne Family Trust | Methods for modeling the structural health of a civil structure based on electronic distance measurements |
| 8773667, | Jan 18 2010 | FARO TECHNOLOGIES, INC | Sphere bar probe |
| 9354043, | Dec 04 2008 | Laura P., Solliday; Sophie Lin, Trustee of the John Michael Payne Family Trust | Methods for measuring and modeling the structural health of pressure vessels based on electronic distance measurements |
| 9983298, | Feb 05 2015 | ASSOCIATED UNIVERSITIES, INC | Fiber optic based laser range finder |
| Patent | Priority | Assignee | Title |
| 3156755, | |||
| 3158674, | |||
| 3194109, | |||
| 3471239, | |||
| 3535024, | |||
| 3671130, | |||
| 3836256, | |||
| 4502785, | Aug 31 1981 | AT & T TECHNOLOGIES, INC , | Surface profiling technique |
| 4595288, | Sep 26 1983 | Litton Systems, Inc | Method and apparatus for measuring deep mirrors |
| 4701049, | Jun 22 1983 | B V OPTISCHE INDUSTRIE DE OUDE DELFT | Measuring system employing a measuring method based on the triangulation principle for the non-contact measurement of a distance from the surface of a contoured object to a reference level. _ |
| 4790651, | Sep 30 1987 | FARO ACQUISITION, LLC; Faro Laser Trackers, LLC | Tracking laser interferometer |
| 5046837, | May 26 1988 | U S PHILIPS CORPORATION | Illumination system |
| 5146085, | May 12 1989 | Canon Kabushiki Kaisha | Encoder with high resolving power and accuracy |
| 5148235, | Feb 21 1990 | Deutsche Forschungsanstalt fur Luft- und Raumfahrt | Michelson interferometer for producing optical path differences by rotating corner cube retroreflectors |
| 5289434, | Sep 18 1992 | Shell Oil Company | Retroreflector apparatus for remote seismic sensing |
| 5446546, | Jul 02 1993 | Boeing Company, the | Laser interferometric single piece force transducer |
| 5530549, | May 24 1994 | FARO TECHNOLOGIES, INC | Probing retroreflector and methods of measuring surfaces therewith |
| 5689812, | Jun 21 1994 | Hitachi, Ltd. | Radio propagation simulation method |
| 5861956, | May 27 1997 | FARO TECHNOLOGIES, INC | Retroreflector for use with tooling ball |
| 5920394, | Sep 01 1995 | KODAK CANADA ULC | Optical coordinate measuring machine |
| 6017125, | Sep 12 1997 | Lawrence Livermore National Security LLC | Bar coded retroreflective target |
| 6313918, | Sep 18 1998 | Zygo Corporation | Single-pass and multi-pass interferometery systems having a dynamic beam-steering assembly for measuring distance, angle, and dispersion |
| 6362468, | Jun 10 1999 | MINATO ADVANCED TECHNOLOGIES INC | Optical unit for detecting object and coordinate input apparatus using same |
| 6420694, | Sep 21 1999 | The Boeing Company | Steerable retroreflective system and method |
| 6661447, | Mar 30 2001 | Heidelberger Druckmaschinen AG | Image-recording device for a printing form having macrooptics of the offner type |
| 6901673, | May 20 2004 | The Boeing Company | Tie-in device for the correlation of coordinate systems |
| 7130056, | Feb 20 2004 | Keysight Technologies, Inc | System and method of using a side-mounted interferometer to acquire position information |
| 7385710, | Apr 15 2002 | Measuring device | |
| 7486707, | Dec 15 2003 | Carl Zeiss SMT GmbH | Optical delay module for lenghtening the propagation path of a light beam and pulse multiplication or elongation module |
| Executed on | Assignor | Assignee | Conveyance | Frame | Reel | Doc |
| Jan 16 2008 | Associated Universities, Inc. | (assignment on the face of the patent) | / | |||
| May 18 2015 | ASSOCIATED UNIVERSITIES, INC | NATIONAL SCIENCE FOUNDATION | CONFIRMATORY LICENSE SEE DOCUMENT FOR DETAILS | 035873 | /0083 |
| Date | Maintenance Fee Events |
| Sep 06 2013 | M2552: Payment of Maintenance Fee, 8th Yr, Small Entity. |
| Sep 05 2017 | M2553: Payment of Maintenance Fee, 12th Yr, Small Entity. |
| Date | Maintenance Schedule |
| Oct 26 2013 | 4 years fee payment window open |
| Apr 26 2014 | 6 months grace period start (w surcharge) |
| Oct 26 2014 | patent expiry (for year 4) |
| Oct 26 2016 | 2 years to revive unintentionally abandoned end. (for year 4) |
| Oct 26 2017 | 8 years fee payment window open |
| Apr 26 2018 | 6 months grace period start (w surcharge) |
| Oct 26 2018 | patent expiry (for year 8) |
| Oct 26 2020 | 2 years to revive unintentionally abandoned end. (for year 8) |
| Oct 26 2021 | 12 years fee payment window open |
| Apr 26 2022 | 6 months grace period start (w surcharge) |
| Oct 26 2022 | patent expiry (for year 12) |
| Oct 26 2024 | 2 years to revive unintentionally abandoned end. (for year 12) |